Camera

ABSTRACT

The present invention relates to the improvement of an exposure control means in a camera having a centralized control system that has a built-in control circuit such as a microprocessor etc. and employing a shutter wherein an optimum exposure is obtained in a way that the exposure is given to the film between the gradual opening of the shutter and the closing thereof and the correlations between the shutter apertures and their corresponding lapse of time form a triangle on the graph. It further relates to the improvement of the exposure control means for flash photographing in a camera employing aforesaid shutter and a bulit-in strobe flash light source.

This application is a continuation of application Ser. No. 697,073,filed 1/31/85.

This application claims priority of Japanese Application No. 20409/1984,filed Feb. 6, 1984, Japanese Application No. 20410/1984, filed Feb. 6,1984, and Japanese Application No. 213464/1984, filed Oct. 9, 1984 under35 USC 119.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the improvement of an exposure controlmeans in a camera having a centralized control system that has abuilt-in control circuit such as a microprocessor etc. and employing ashutter wherein an optimum exposure is obtained in a way that theexposure is given to the film between the gradual opening of the shutterand the closing thereof and the correlations between the shutterapertures and their corresponding lapse of time form a triangle on thegraph. It further relates to the improvement of the exposure controlmeans for flash photographing in a camera employing aforesaid shutterand built-in strobe flash light source.

2. Description of the Prior Art

With the spread of electronics used in a camera, various functions of acamera have been diversified with their performance improved. While theshutter that is a basis of an exposure control is still continuing itsconventional construction and no remarkable progress has been observedin particular. The majority of the program control shutter which is ashutter-cum-diaphragm for the present small-sized camera is the onewherein the gradual opening of the shutter gives an exposure to the filmand the closing thereof gives an optimum exposure and the correlationsbetween the shutter apertures and their corresponding lapse of time forma triangle on the graph The shutters of such type are disclosed inJapanese Patent Examined Publication Nos. 18111/1971 and 11947/1969 forexample.

In the technology of aforesaid shutter, the capacitor is charged withphotoelectric current from the light-responsive element from the momentof the start of shutter opening and then the shutter closing isperformed when the voltage charged in the capacitor reaches a certainlevel of voltage, namely, when the optimum exposure is given to thefilm. This system is publicly known and therefore the detaileddescription thereof will not be made here but it has demerits on thepoints of characteristics of light-responsive element and complicatedmechanical structure of the shutter, as itemized below.

(1) When CdS is used as a light-responsive element, the γ value thatrepresents the relation between the quantity of light and the resistancevalue for CdS needs to be 0.5.

(2) There is a limitation for the opening speed of the shutter.

Despite the spread of electronics in a camera mentioned above, theshutter itself still consists obstinately of mechanical factors whichhave prevented the simplification of camera structure.

On the other hand, an aperture value F that gives an optimum exposure inflash photographing is obtained, as is generally known, from theequation of F=GNO/L, where "GNO" is a guide number of a strobe flash and"L" is a subject distance. Following two ways have been known as anapplication of the equation.

(1) An aperture is to be changed according to the subject distance.Namely, it is a method of so-called flash-matic mechanism wherein anaperture diameter is changed being interlocked with the turning of afocusing ring.

(2) A method that employs a shutter-cum-stop and causes a strobe flashto emit light during the course of gradual opening of the shutterranging from the closing to the opening thereof and changes its emissiontiming according to the subject distance.

The former method makes it very difficult to photograph using a DX filmand it is actually impossible to incorporate into a small-sized camerathe flash-matic mechanism that makes the photographing on the DX filmpossible, which is a demerit. The mechanism that detects the ISO speedfrom the DX film and changes the stop value through the mechanicaldriving thereof using the electric signal converted from the ISO speeddetected requires electro-magnetic devices such as a motor, a magnet andothers as a driving source and thereby it is actually difficult toincorporate such mechanism into a small-sized camera.

Since the control of emission timing for strobe flash is madeelectrically in the method of (2), it is easy to introduce theinformation of ISO speed obtained from a DX film into the control systemand therefore the method (2) is suitable for the use of DX films.

However, the following problem is caused by the application of themethod (2) to a camera. An emission timing of the strobe flash may beobtained through the calculation that employs the aforesaid equation andthe correlation between the shutter aperture and time shown in FIG. 1.Heretofore, the calculation has been performed for the determination ofthe emission timing of the strobe flash under the assumption that theshutter aperture changes linearly and ideally with the lapse of time asshown in FIG. 1. However, it is impossible for the actual shutter tohave such an ideal aperture characteristic. It is known that the seriousnonlinearity in the aperture characteristic is caused by the type of theshutter mechanism employed or the like and it has become clear that theemission timing obtained from the simple calculation like the oneexplained above can not provide an optimum exposure due to the aforesaidnonlinearity.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to provide, using the technologyof integrated circuit such as a microcomputer or the like, a simplifiedexpose control means for camera, especially to provide an exposurecontrol means satisfying the following.

(1) Simplification of mechanical structure of the shutter

(2) To remove the restriction for the selection of light-responsiveelements and photometry circuits

(3) Introduction of film speed and simplification of exposure controlaffected by the change in film-speed

The present invention has been devised in due consideration of theproblems in the prior art explained above and its object is to providean exposure control means for artificial light that provides an optimumexposure with a small error in exposure in the flash photographing whenthe aforesaid method (2) is applied to a camera.

The present invention is to provide a camera comprising:

a photometry means that measures the brightness of a subject andproduces the measurement results as a subject brightness information;

a shutter device the aperture of which gradually opens from theclosed-shutter condition to the full-open condition and then changes tothe closing operation with a shutter-closing signal; and

an exposure control means that receives at least aforesaid subjectbrightness information and controls the operation of aforesaid shutterdevice based on said subject brightness information;

wherein, aforesaid exposure control means has a memory means wherein theclassification of subject brightness and timing information for theshutter-closing instruction for each class of subject brightness arestored in the form of a table and a timing information for theshutter-closing instruction corresponding to the subject brightnessinformation inputted is selected from said table for the exposure.Further, the present invention is to provide a camera comprising:

a film speed setting means that produces the speed information of thefilm loaded in the camera;

a strobe flash emission device; and

a judgment means that judges whether the strobe flash emission device isoperating or not;

wherein, said camera has a memory means wherein a table corresponding tothe foregoing is stored and the timing information for theshutter-closing instruction based on the information of the foregoingand/or the emission timing for the strobe flash emission device areselected from aforesaid table.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and (b) show the relational characteristic between theshutter and the quantity of the exposure.

FIGS. 2(a) and (b) show the basic block diagram of the presentinvention,

FIG. 3 and FIGS. 5(a) and (b) are the circuit diagram of the exposurecontrol device of the present invention,

FIG. 4 shows the correction between subject brightness andexperimentally obtained photometry time.

FIG. 6 shows an operation program of the exposure control circuit of thepresent invention,

FIG. 7 is a plane view of the shutter mechanism section of the presentinvention,

FIGS. 8(a) and (b) are the circuit diagram for the main part of theexample of the present invention,

FIGS. 9(a) and (b) show a flow chart of the present invention and

FIGS. 10(a) and (b) the correlation between the shutter aperture and theemission timing in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As explained above, the aperture characteristic of the shutter for thelapse of time in a diaphragm-shutter is not a straight line shown inFIG. 1 but is a curved line deviated from the straight line as shown as"l" in FIG. 1'.

Regarding the aperture characteristic, however, its dispersion amongshutters is small and in the case of a shutter of a particular typebased on a peculiar design, the dispersion of the characteristic amongshutters is small, owing partly to the quality control for massproduction, thus stable characteristics may be obtained. Massmeasurement of the shutters in the example explained later offered ameasured value of 20 ms±2 ms as a dispersion in the time required by theshutter to open to the maximum aperture diameter and the dispersion inexposure quantity caused by the aforesaid dispersion in the time issufficiently within the latitude of the film and therefore is allowable.

If the stability in the time-wise characteristic of the shutter apertureopening is used, it is possible to obtain the time ranging from thestart of shutter opening to the start of shutter closing (hereinafterreferred to as the shutter time) necessary for giving an optimumexposure to the film for each subject brightness as a common data foraforesaid shutter of peculiar type. Following Table 1 shows thecorrelation between the brightness of a subject nd the shutter time bothobtained experimentally.

In the present example, the exposure control range covers from EV 8.5 toEV 16 in terms of subject brightness and all EV values from EV 8.5 to EV16 with a step of 0.5 EV and their corresponding shutter time are storedunder the basis of the unit of APEX (Additive system of PhotographicExposure) system. However, the exposure control range and the width of astep may freely be established. In the table, the maximum shutter timeis limited up to 20 ms for the prevention of unintentional movement ofthe hands in photographing and is limited down to 2.6 ms, on the otherhand, because it is difficult to control the minimum shutter aperturecorresponding to the shutter time of 2.6 ms or less.

                  TABLE 1                                                         ______________________________________                                        Subject Brightness and Shutter Time                                           subject brightness                                                                           film speed                                                     EV       zone      ISO 100  ISO 200  ISO 400                                  ______________________________________                                        16       0         2.6    ms  2.6   ms   2.6  ms                                       1         3.3        2.6        2.6                                  15       2         3.8        2.6        2.6                                           3         4.6        3.3        2.6                                  14       4         5.0        3.8        2.6                                           5         6.0        4.6        3.3                                  13       6         6.8        5.0        3.8                                           7         7.8        6.0        4.6                                  12       8         8.8        6.8        5.0                                           9         11.5       7.8        6.0                                  11       10        15.2       8.8        6.8                                           11        20.0       11.5       7.8                                  10       12        20.0       15.2       8.8                                           13        20.0       20.0       11.5                                  9       14        20.0       20.0       15.2                                          15        20.0       20.0       20.0                                 ______________________________________                                    

FIG. 2a shows a block diagram representing the actions of the camera ofthe present invention wherein the action of the shutter device iscontrolled by the subject brightness information obtained by thephotometry means.

The photometry means 1a detects the brightness of subject through thelight-responsive element and sends the brightness information to thecontrol means 2a.

The information means 3a sends the information of the film speed andothers to the control means 2.

The memory means 4a wherein the shutter aperture characteristics shownin the above table is already stored.

The control means 2a determines, through the selection from the memorymeans 4a or the selection processing therefrom, the shutter timenecessary for giving the optimum exposure to the film based on thevalues from the photometry means 1a and the information means 3a.

As stated above, the shutter time is stored temporarily in the controlmeans 2a and these stored values control the shutter section 5a when theexposure control is performed later, thus photographing is made.

Though the exposure control means is divided into the aforesaid blocksfor the purpose of clear explanation, it is possible to combine theblocks into one IC using the integrated circuit and the microcomputermakes the merits of the present invention notable, in particular.

FIG. 2(b) is a block diagram of the actions of the camera of the presentinvention having the photometry means and strobe flash device whereinthe strobe flash emission is made concurrently with the operation of theshutter device.

The photometry means 1b detects, through its light-responsive element,the subject brightness and sends the brightness information to thecontrol means 2b.

The information means 3b sends the information such as the film speed,the use of strobe flash and others to the control means 2b.

The memory means 4b stores the shutter aperture characteristic shown inthe aforesaid table. The Table 2 shown below indicates the shutter timestored in the memory means 4b and the generation timing for triggersignals of strobe flash. The data in Table 2 were not obtained fromrelational expressions that gives an optimum exposure concerning theparameters such as subject brightness, diaphragm, shutter time, subjectdistance, guide number and film speed etc. both for AE and the use ofstrobe flash but were obtained from the results of measurement on theshutters actually prepared.

The control means 2b determines, through the performance of selection orselection processing from the memory means 4b, the shutter timenecessary for giving an optimum exposure to the film based on the valuesfrom the photometry means 1b and the information means 3b.

As stated above, the shutter time is provisionally stored in the controlmeans 2b and later when the exposure control is made, the storage valuecontrols the shutter section 5b, thus photographing is performed.

Therefore, it is difficult for the conventional mechanical emissionmeans for artificial light to emit the light while the shutter isopening but it is possible for the method of the present invention toset the emission which may be made at an arbitrary aperture diameterduring the shutter-opening. Namely, when the strobe flash is used as anauxiliary light, it is possible to set relatively freely the ratio ofthe natural light quantity to the auxiliary light quantity and thus itis possible to photograph for photographs of good quality.

                                      TABLE 2                                     __________________________________________________________________________    Photometry Zone Value and Shutter Time                                        (unit: m sec)                                                                 subject                                                                             ISO 100      ISO 200      ISO 400                                       brightness                                                                             strobe flash is used                                                                       strobe flash is used                                                                       strobe flash is used                       EV zone                                                                             AE AF short                                                                           AF long                                                                            AE AF short                                                                           AF long                                                                            AE AF short                                                                           AF long                               __________________________________________________________________________    16 0  2.6                                                                              2.6  2.6  2.6                                                                              2.6  2.6  2.6                                                                              2.6  2.6                                      1  3.3                                                                              3.3  3.3  2.6                                                                              2.6  2.6  2.6                                                                              2.6  2.6                                   15 2  3.8                                                                              3.8  3.8  2.6                                                                              2.6  2.6  2.6                                                                              2.6  2.6                                      3  4.6                                                                              4.6  4.6  3.3                                                                              3.3  3.3  2.6                                                                              2.6  2.6                                   14 4  5.0                                                                              5.0  5.0  3.8                                                                              3.8  3.8  2.6                                                                              2.6  2.6                                      5  6.0                                                                              6.0  6.0  4.6                                                                              4.6  4.6  3.3                                                                              3.3  3.3                                   13 6  6.8                                                                              6.8  6.8  5.0                                                                              4.6  5.0  3.8                                                                              3.3  3.8                                      7  7.8                                                                              6.8  7.8  6.0                                                                              4.6  6.0  4.6                                                                              3.3  4.6                                   12 8  8.8                                                                              6.8  8.8  6.8                                                                              4.6  6.8  5.0                                                                              3.3  5.0                                      9  11.5                                                                             6.8  11.5 7.8                                                                              4.6  7.8  6.0                                                                              3.3  6.0                                   11 10 15.2                                                                             6.8  15.2 8.8                                                                              4.6  8.8  6.8                                                                              3.3  6.8                                      11 20.0                                                                             6.8  20.0 11.5                                                                             4.6  11.5 7.8                                                                              3.3  6.8                                   10 12 20.0                                                                             6.8  20.0 15.2                                                                             4.6  15.2 8.8                                                                              3.3  6.8                                      13 20.0                                                                             6.8  20.0 20.0                                                                             4.6  20.0 11.5                                                                             3.3  6.8                                    9 14 20.0                                                                             6.8  20.0 20.0                                                                             4.6  20.0 15.2                                                                             3.3  6.8                                      15 20.0                                                                             6.8  20.0 20.0                                                                             4.6  20.0 20.0                                                                             3.3  6.8                                   __________________________________________________________________________

Now, the light-responsive element to be used in the present inventionand the exposure control by means of the information obtained by thephotometry means will be explained in detail.

FIG. 3 is an explanatory circuit diagram showing the principle of thephotometry means wherein the current corresponding to the quantity oflight received by the light-responsive element or the light-responsiveelement unit marked as PC in the diagram is stored in the capacitor Cfrom the moment of the start of photometry (switch SW OFF) and then thevoltage of the capacitor C is compared with a reference voltage Vref bythe comparator COM, thus the time ranging from the start of photometryup to the moment when the capacitor voltage becomes equal to thereference voltage Vref is measured. The time is actually counted by thetimer 113 whose counting is started with the timing of "OFF" action ofthe switch SW and completed when the voltage of the capacitor C isequalized with the standard voltage In the control circuit, on the otherhand, the correlation between the various quantity of light received bythe light-responsive element PC and various time periods measured in theaforesaid manner is stored in advance and thereby the quantity of thelight may be obtained. The foregoing is a function of the exposurecontrol means for camera of the present invention.

The circuit in FIG. 3 may be applied intact to the example employing themicroprocessor (hereinafter referred to as "micom") wherein atransistor, CdS and a timer are built as the switch SW, thelight-responsive element PC and a control circuit respectively. Namely,the light-responsive element CdS and the integrating capacitor C areconnected in series and the integrating capacitor C and the switchingtransistor 112 are connected in parallel. If the switching transistor isturned on prior to the photometry, the capacitor C is discharged and itsvoltage goes down to zero. Next, if the switching transistor 112 isturned off, the capacitor is charged from CdS at the speed correspondingto the subject brightness and thereby the voltage at the capacitor goesup. Namely, the photometry is started. The voltage of the capacitor iscompared with the standard value Vref by the comparison circuit COM andthe comparison output therefrom is inputted in the micom which is acontrol circuit. Based on this inputted signal, the micom detects,through its built-in timer, the time period from the start of thephotometry to the moment when the output from aforesaid comparisoncircuit COM tells that the voltage of the capacitor has been equalizedwith the standard value Vref.

With power source voltage Ve, reference voltage Vref, resistance valueof CdS Rcds and capacity of integrating capacitor C, the time T (that iscalled the photometry time) ranging from the transistor 112 being openedup to the moment of reaching the reference value is: ##EQU1## andfurther, if Vref is determined through the resistive dividing,

    T=CRcds ln (1-k)

thus, the photometry time is independent of the power source voltage andis determined only by the resistance of CdS, the capacity of capacitorand the resistive dividing ratio.

Since the resistance of CdS is determined by the quantity of lightreceived, the brightness of the subject is obtained by detecting thephotometry time T. Namely, the correlation between the quantity of lightand the photometry time is stored in the Micro Processor Unit(hereinafter referred to as MPU) 111 in advance and the brightness ofthe subject can be obtained by selecting the memory value using thephotometry time. The correlation between the brightness of the subjectand the photometry time obtained experimentally in the present exampleis shown in FIG. 4 and Table 3 shows the example of the memory in whichthe correlation between the photometry time T₁ and the brightness of thesubject corresponding to the photometry time is stored in the MPU 111with an interval of 1/2EV step, and the interval of the step can freelybe established.

                  TABLE 3                                                         ______________________________________                                        Subject Brightness and Photometry Time                                        zone      T.sub.1 (ms)                                                                           brightness of subject (EV)                                 ______________________________________                                        0           -4.8     -153/4                                                   1         4.8-5.7  153/4-151/4                                                2         5.7-6.8  151/4-143/4                                                3         6.8-8.0  143/4-141/4                                                4         8.0-9.5  141/4-133/4                                                5          9.5-11.2                                                                              133/4-131/4                                                6         11.2-13.8                                                                              131/4-123/4                                                7         13.8-16.5                                                                              123/4-121/4                                                8         16.5-20.0                                                                              121/4-113/4                                                9         20.0-24.5                                                                              113/4-111/4                                                10        24.5-30.0                                                                              111/4-103/4                                                11        30.0-37.0                                                                              103/4-101/4                                                12        37.0-45.0                                                                              101/4-93/4                                                 13        45.0-55.0                                                                              93/4-91/4                                                  14        55.0-66.0                                                                              91/4-83/4                                                  15        66.0-    83/4-81/4                                                  ______________________________________                                    

The merits of the exposure control means explained above are listedbelow.

(1) The γ value of CdS needs not be specified.

(2) The resistance value of CdS corresponding to a certain quantity oflight can easily be corrected with the use of the resistive dividingratio.

(3) The circuit construction is simple.

(4) The exposure control means is not power source voltage-dependent.

On the other hand, the demerit is that the dispersion in the γ value ofCdS affects the exposure control means. But the dispersion is in thelevel negligible for photographing, therefore it is not essentially aproblem.

Though the charging time for the capacitor is measured in the exampleexplained above, the brightness of the subject may also be obtained inthe manner wherein the capacitor is charged in advance, the charging isstopped and discharging through the light-responsitive element isstarted concurrently with the start of photometry, the time required fordischarging down to the reference voltage is measured and then themeasured time is compared with the memory value of subject brightnessand discharging time stored in the control circuit. The circuit diagramof this example is shown in FIG. 5(a) in which the numeral 121 is acontrol circuit employing MPU, 122 is a transistor that stops thecharging concurrently with the start of photometry, 123 is alight-responsive element CdS, 124 is a capacitor and 125 is a comparisoncircuit that compares the voltage after discharging in the capacitor 124with the reference voltage Vref. The MPUs 111 and 121 of the exposurecontrol means shown in FIG. 3 and FIG. 5(a) respectively operateaccording to the program shown in FIG. 6.

Further, FIG. 5(b) shows an example of the circuit in which thelight-responsive element other than CdS such as photo diode, phototransistor or selenium element etc. is used. In this circuit, thephoto-electric current that flows through the photo transistor 133 isstored in the capacitor 134 thereby the exposure control is similarlyattained. In this case, however, it is naturally possible to organize anexposure control means with a light-responsive unit wherein the functionsuch as the improvement in characteristics against temperature of thelight-responsive element or the amplification of photo-electric currentis added by providing at need the circuit that converts or amplifiessignals of the current and voltage etc. generated in thelight-responsive element, in addition to the function that thelight-responsive element itself generates only photo-electric current.

In each example mentioned above, the comparison circuit is especiallyused to serve the convenience of explanation but when the transistor isused in the input step of the control circuit, it is possible tosimplify the circuit construction by using the base emitter voltage ofthe transistor. Likewise, also in the case when a C-MOS circuit is usedas an input step of the control circuit, the threshold voltage of theC-MOS may be utilized.

Regarding the exposure control means and the photometry means bothrelating to the present invention, an explanation has been made aboveindividually focusing on Tables 1, 2 and 3. However, it may be clear forthose skilled in the art that all of Tables 1, 2 and 3 do notnecessarily need to be stored. Namely, if the table showing the relationbetween the classification of the photometry time {corresponding to T₁(ms) in Table 3} corresponding to the classification of the subjectbrightness and the shutter time {corresponding to the shutter time (ms)in Tables 1 and 2} corresponding to aforesaid photometry time only isstored, the timing information for the shutter-closing instructioncorresponding to the subject brightness information (i.e. aforesaidphotometry time) obtained by the photometry means can be obtained fromthe table.

The embodiment of the present invention will be explained next. Theembodiment was embodied in the lens shutter which uses 135 film and aplane view of the example of shutter mechanism section is shown in FIG.7 and a circuit diagram of main parts of the example of the camera thatcontrols an exposure using the information obtained from the photometrymeans is shown in FIG. 8(a).

In FIG. 8(a), when the first step S₁ of the release switch in 2-stepconstruction is depressed, the entire circuit is energized, the MPU 8starts operating and an automatic focusing detection (AF) is firstperformed. The AF system of the present invention is performed throughthe range-finding circuit 7 in which the infrared LED 71 is caused toemit light and the infrared reflected light on the subject is receivedby the position sensitive element 72 for range-finding. The positionsensitive element 72 is composed of two light-responsive elements whichproduce different current each other depending on the different quantityof light received. These currents are amplified by the AC amplificationcircuit 75 and 76 respectively and then the result therefrom is comparedwith an electric signal corresponding to a certain distance between asubject and a camera where the currents from the two light-responsiveelements are equal, thus the distance information is obtained.

Then, the MPU 8 measures the brightness of the subject through thephotometry means 1 explained earlier.

Now, the information of the film speed switches 32 and 33 located in theinformation means 3 are introduced into the MPU 8. In the presentexample, the film speed can be selected by the MPU with the use of 2-bitsignal because the film speed is limited to 3 kinds of ISO 100, ISO 200and ISO 400. Incidentally, the following was set up. "0" signal onswitch 32 and "0" signal on switch 33 for ISO 100 "0" signal on switch32 and "1" signal on switch 33 for ISO 200 "1" signal on switch 32 and"1" signal on switch 33 for ISO 400

With all the information necessary for determining the shutter timeintroduced as stated above, the MPU 8 determines the shutter timeaccording to the aforesaid table. Then, if the second step of therelease switch is not depressed for some reason, the cycle returns tothe photometry step again. Aforesaid operation steps of the MPU areshown as the schematic flow chart in FIG. 9(a).

The method of Table 1-consultation for the selection of shutter time inthe schematic flow chart is easy for those skilled in the art to conductand following is a brief explanation of one example. The contents of thetable of shutter time data mentioned above are stored in succession inthe memory addresses on the Read-Only-Memory located in the MPU 8 andthen the range of memory addresses for data selection is limited firstto some degree according to the film speed information and thus thefirst or the last memory address in the range is determined. After that,the brightness of the subject selects the particular data addresslocated with a certain distance from the first or the last memoryaddress.

Following the first step of the release switch depressed, if S₂ which isthe second step of the release switch is depressed and thereby S₂ isclosed electrically and the exposure-control-start-signal is produced,the MPU 8 first energizes the shutter magnet 51 and then energizes AFmagnet 34 based on the value stored after the range finding made by theAF circuit 7 and causes the photographing lens to rotate toward thefocusing position, and after it has rotated and moved to the prescribedposition, the MPU 8 stops energizing AM magnet 31 and the lever thatturns the shutter-locking member being affected by the rotation of thelens moves, which means that the shutter-locking member is released onlyafter the photographing lens has been fixed.

Now, the mechanism and operation of exposure control will be explainedreferring to FIG. 7. The numeral 90 in the figure shows the optical axisof the photographing lens, 91 and 92 are the shutter blades A and Bperforming the opening and closing of shutter aperture and the figureshows the situation of closed shutter and shutter opening is performedwhen the shutter blade A91 is moved toward left and at the same time theshutter blade B92 is moved toward right. In the structure of theexposure control, the shutter opening is performed by the shutter bladelever 93 rotating counterclockwise.

As stated above, if the release lever 95 which is a shutter-lockingmember is released to turn counterclockwise, the shutter blade lever 93rotates counterclockwise and at the same time the shutter blade A91interlocking with the shutter blade lever 93 and the shutter blade B92move toward the shutter opening. Then, the shutter-trigger switch 99{corresponding to ST in FIG. 8(a)} that is preset so that it is turnedOFF when the shutter forms a pinhole aperture is actuated.

The MPU 8, on the other hand, keeps detecting the shutter-trigger-switch99 to be turned OFF and if it detects the OFF, it calculates the shuttertime based on the data selected or selection-processed from the Table 1.

At the moment when the release lever 95 is released, the shutter-magnet98 {corresponding to 51 in FIG. 8(a)} is already under the electrifiedcondition and thereby the magnet lever 97 is prevented by the magneticforce from rotating. Under such condition, the shutter keeps opening itsaperture until the MPU 8 finishes its calculation of the shutter time.Then, concurrently with the completion of shutter time calculation, theMPU 8 stops electrifying the shutter magnet 98. With a disappearance ofthe magnetic force of the shutter magnet 98, the magnet lever 97 isrotated counterclockwise by the spring force and thereby theshutter-closing-lever-hook 96 is rotated clockwise. Then, theshutter-closing-lever 94 which has been locked by theshutter-closing-lever-hook 96 rotates clockwise and at the same timecauses the shutter blade lever 93 to rotate clockwise opposite to thedirection of shutter opening, thus the shutter is caused to close and anexposure is completed.

The mechanism section which has completed the aforesaid shutteroperation turns the magnet lever 97 clockwise through the other chargingmember (not shown) and causes it to be hooked by the release lever 95.After that, the mechanism section turns the shutter-closing lever 94counterclockwise and causes it to be hooked by theshutter-closing-lever-hook 96, thus the shutter-charging is completed.

A concrete example of the camera having the photometry means and thestrobe flash device and strobe emission is made concurrently with anoperation of the shutter device in said camera of the present inventionwill be explained as follows. The example was embodied in the lensshutter in which a 135 film is used and the shutter mechanism section isidentical to FIG. 7 explained already and FIG. 8(b) shows a circuitdiagram for the main section of the example.

When a strobe flash is used for photographing, the power switch So forstrobe flash is turned ON and thus the strobe flash circuit 6 iselectrified and the strobe flash capacitor 61 is charged by the voltageboosted up to about 300 V. After the capacitor has been charged, theneon tube 63 is lit through the resistance 62, which indicates that thepreparation for strobe flash has been finished. At this point, theswitch 31 in the information means 3 that opens or closes concurrentlywith the switch So is also turned ON and thereby the information of theswitch 31 for strobe flash are set in the MPU 8 provided with both thecontrol means 2 and the memory means 3.

Then, if the first step S₁ of the release switch which is of a two-stepstructure is pressed, the entire circuit is electrified and thereby theMPU 8 starts operating and performs first the automatic focusing (AF).An AF of the present example is performed through the photometry circuit7 in which the infrared LED 71 is caused to emit and then the infraredreflected light from the subject is received by the position-detectingelement 72 for range-finding. While the MPU 8 waits for the infraredemission capacitor 73 to be charged and when the charging has beenmostly finished, the infrared emission transistor 74 is closedelectrically by the MPU 8 and thereby the infrared emission capacitor 73is discharged and the infrared LED 71 is lit. Infrared rays emittedreflect on the subject and then received by the position-detectingelement 72 which is composed of two light-responsive elements and thecurrent running through each light-responsive element differs each otherdepending upon the quantity of light received by each element. Thesecurrents are amplified respectively by AC amplifying circuits 75 and 76and then are compared in the comparison circuit 78 with the electricsignal for the standard distance which is a switching point between longand short distances and thus the distance information may be obtained.

The distance information which is an output signal from the comparisoncircuit 78 is inputted into the MPU 8 and the best timing for the MPU 8to receive this input signal in the present example is about 100 μ secafter the infrared emission. The distance information received in theaforesaid timing is stored in the MPU 8.

Next, the MPU 8 measures the subject brightness through the photometrymeans 1 explained already.

Now, the MPU 8 introduces the information of film speed switches 32 and33 located in the information means 3. In the present example, the filmspeed information is read from the film container of a DX type, namely,the film container of a DX type is mounted on a camera and the filmspeed information is automatically read for each photographing action.In the present example, the type of film to be used is limited to threekinds of ISO 100, ISO 200 and ISO 400 and therefore each film speed canbe selected by the MPU using a two-bit signal. Incidentally, thefollowing was set up.

"1" signal on switch 32 and "0" signal on switch 33 for ISO 100

"0" signal on switch 32 and "0" signal on switch 33 for ISO 200

"1" signal on switch 32 and "1" signal on switch 33 for ISO 400

With all the information necessary for determining the shutter timeintroduced as stated above, the MPU 8 determines the shutter time andemission timing for strobe flash according to the aforesaid table. Then,if the second step of the release switch has been pressed, the MPU 8performs exposure control and if it has not been pressed, the cyclereturns to the photometry step again. Aforesaid operation steps of theMPU are shown as the schematic flow chart in FIG. 9(b).

Aforesaid Table 2 used in the present example is a table of the shuttertime allowing the photographing in the natural light as well as adaylight synchronization which is the photographing in strobe flash(natural light+strobe flash photographing). The method of daylightsynchronization employs a known concept of smaller aperture-priority.Smaller aperture-priority is a method wherein the smaller aperture(smaller stop) is preferred from the maximum aperture for the stopdetermined through AE and the stop value determined by both the guidenumber of strobe flash and the subject distance and then the strobeflash emission is made at the point of aforesaid stop value and at thesame time the shutter-closing action is made. In this method, theshutter-closing action may be made concurrently with the strobe flashemission, therefore the emission timing for strobe flash is notindicated on the aforesaid table in the present example.

In Table 2, the shutter time values not greater than 2.6 m sec areindicated as 2.6 m sec and the ones not smaller than 20 m sec areindicated as 20 m sec. The reason for the foregoing is that it isdifficult to control the shutter under the aperture diameter not greaterthan the diameter that represents F22 corresponding to the shutter timeof 2.6 m sec. The reason for the limitation up to 20 m sec, on the otherhand, is to prevent the camera-shake. Namely, within the rangecorresponding to 20 m sec, a low-brightness-warning (not shown in thefigure) is given out thus calling a photographer's attention to flashphotographing. Further, the constant shutter time on the low-brightnessside in the strobe flash mode is the result of what the stop value basedon the subject distance in the flash photographing explained earlier ispreferred.

Following the first step of the release, if the second step S₂ of therelease is closed to be the state of ON and anexposure-control-start-signal is given out, the MPU 8 electrifies, afterelectrifying the shutter magnet 51, the AF magnet 34 according to thememory value measured through the AF circuit 7 for the photographinglens to turn to the focal position and then stops electrifying the AMmagnet 31 for the photographing lens to be fixed when it arrives at apredetermined position after its movement by turning. With this turningof the lens, the lever that causes the shutter-holding member to rotatealso moves, thus the holding by the shutter-holding member is releasedafter the photographing lens has been fixed.

Now, the construction and operation of the exposure control has beenexplained referring to FIG. 7. In the figure, the numeral 90 shows theoptical axis of the photographing lens and 91 and 92 are the shutterblades A and B that take charge of shutter opening respectively. Thefigure shows the state of the closed shutter and the shutter is openedwhen the shutter blade A 91 moves to the left and the shutter blade B92moves to the right simultaneously. In the construction, theshutter-opening is performed when the shutter-blade-lever 93 rotatescounterclockwise.

As stated above, if the release-lever 95 that is the shutter-holdingmember is released and rotates counterclockwise, the shutter-blade-lever93 rotates counterclockwise concurrently with the movements towardsshutter-opening of the shutter blade A91 and shutter blade B92 bothbeing interlocked with the shutter-blade lever 93. And then, the shuttertrigger switch 99 {corresponding to ST in FIG. 8(a)} that is set so thatit is turned OFF at the moment when the shutter opening reaches thepreset opening is operated.

The MPU 8, on the other hand, keeps detecting the shutter trigger switch99 to be turned OFF and after the detection of the OFF thereof, theshutter time is counted by the MPU 8 based on the data selected orselection-processed through Table 2.

At the moment when the release lever 95 is released, the shutter magnet98 (corresponding to 51 in FIG. 4) is excessively electrified andtherefore, the magnet lever 97 is prevented by the magnetic force fromrotating. Under such condition, the shutter keeps opening until the MPU8 completes counting the shutter time. Concurrently with the completionof shutter time counting, the MPU 8 turns ON the transistor 64 locatedin the strobe flash circuit 6 in the case of flash photographing, turnsON the thyrister 65 that triggers strobe flash and thus the strobe flashemission is performed. For the natural light photographing, it isnaturally unnecessary to cause such strobe flash signals to be produced.

The MPU 8 cuts electrification through the shutter magnet 98concurrently with the completion of shutter time counting. When theshutter magnet 98 loses its magnetic force, the magnet lever 97 isrotated counterclockwise by the spring force and the closing lever hook96 rotates clockwise. The shutter closing lever 94 held by the closinglever hook 96 rotates clockwise and at the same time causes the shutterblade lever 93 to rotate clockwise which is opposite to the direction ofshutter opening, thus the shutter is closed and the exposure iscompleted.

The mechanism section that has completed aforesaid shutter operationcauses the magnet lever 97, with the help of the other charging member(not shown), to rotate clockwise and to be held by the release lever 95.After that, the shutter closing lever 94 is caused to rotatecounterclockwise and to be held by the closing lever hook 96, thus theshutter-winding is completed.

In the aforesaid example, the shutter time values obtained from thecombination of information from all information means and photometryinformation are stored in the memory means 4 and any one of the shuttertime values is selected by each information but it is also possible tocontrol the exposure by storing only a part of the data utilizing theprocessing function and the judgment function of the MPU 8. As for theISO information of film speed, the difference between ISO 100 and ISO200 corresponds to 1 EV of brightness information as is clear from theaforesaid Table 2, the switching of ISO information can easily be donethrough the simple processing.

Further, when the stop value for the low brightness in the smalleraperture-priority system with the use of strobe flash is preferred, ifthe photometry information from the distance information and theinformation of existence of strobe flash used is not higher than thespecific EV, the shutter time can be constant. In the example of thepresent Table 2, when the film with the speed of ISO 100 is used and thestrobe flash is used for the short subject distance, the shutter timecan be 6.8 m sec which is constant for the photometry information nothigher than EV 13.

As stated above, simple processing enables the ISO information to beswitched between ISO 100 and ISO 200 for example and therefore theinformation of subject brightness and shutter time for only one of thefilm speeds have only to be stored. Consequently, the capacity of thememory means 4 can be small but the processing and judgment need to beperformed by the MPU 8, therefore, it is effective when the informationfrom the information means 3 is much in amount.

In the exposure control system employing smaller aperture-priority as amethod of daylight synchronization mentioned earlier, it is notnecessary to store the strobe flash emission timing in the memory means4 in particular because the strobe flash emission timing synchronizes,as shown in FIG. 10(a), with the closing action of the shutter.Therefore, it has a merit that the capacity of the memory means 4 can besmall. On the other hand, as a demerit of the smaller aperture-prioritysystem, a photograph with an over-exposure by 1 EV may sometimes beobtained theoretically. This phenomenon corresponds to the occasionwhere the F value determined through AE is identical to the F valuedetermined by the information of subject distance for flashphotographing.

In order to avoid such an over-exposure by 1 EV, therefore, the memorycapacity of the memory means 4 may be increased for the storage whicharranges the strobe flash timing in the case of aforesaid conditions sothat strobe flash emits with a timing corresponding to the aperture thatis smaller by 1 EV equivalent than the F value determined by the subjectdistance information. In FIG. 10(b), this emission timing isillustrated.

In the example explained above, due to the shutter mechanism allowingthe aperture-time characteristic which is relatively stable, it ispossible to obtain photographs of fine quality without using thecorrection means in particular. However, it is necessary to correct thedispersion of aperture-time characteristic in the following cases.

(1) Photographs of higher quality are needed.

(2) The aperture-time characteristics are unstable owing to the costreduction and others.

In the method to correct the dispersion of aperture-time characteristic,plural tables of aperture-time characteristic may be stored in thememory means 4, the aperture-time characteristic of the shutter ismeasured in the production of the camera, the control means 2 isinstructed, according to the measured value, to select the peculiartable from the correction means, thus the control means 2 selects theparticular value of shutter time and strobe flash emission timing basedupon the value of the correction means.

Likewise, the means which is equal to the aforesaid correction means maybe taken even when the aperture-time characteristic of the shuttervaries in accordance with the change in temperature. Namely, the valuesobtained by the temperature detecting means are inputted to the controlmeans 2 and at the same time plural tables corresponding to thetemperature difference are stored in the memory means 4, thus theshutter time may be selected based on the data obtained by thetemperature detecting means.

Incidentally, the two-step control as an automatic focusing controlmakes the explanation easy in the present example but it is naturallypossible to improve the exposure accuracy for the natural lightphotographing complying with the multi-step control. Further in thestrobe flash photographing, it is possible to cause the strobe flash toemit at any time while the shutter is opening and therefore it ispossible to change the balance of the quantity of light contributing tothe exposure between the natural light and the strobe flash light.

[Effects of the Invention]

Utilization of a digital integrated circuit, especially of a MPU as thecontrol function in a camera of the present invention explained aboveproduces a remarkable effect. The camera of the present invention makesit possible to simplify the mechanical structure of the shutter, causesthe introduction of film speed and the exposure control after thechangeover of film speed to be performed easily, makes the variousexposure control especially with the use of artificial light such as thestrobe flash light and others possible, gives a good balance betweenelectrical elements and mechanical elements to the camera havingelectronics used therein and provides an exposure control means forflash photographing which offers good results of photographing even forthe flash photographing.

What is claimed is:
 1. A camera comprising:a photometry means thatmeasures the brightness of a subject and produces the measurementresults as a subject brightness information; a film speed-setting meansthat produces the speed information of a film to be set on the camera; adiaphragm-shutter device the aperture of which gradually opens from theclosed-shutter condition to the full-open condition and then changes tothe closing operation with a shutter-closing signal; and an exposurecontrol means that receives at least aforesaid subject brightnessinformation and film speed information and controls for operation ofaforesaid shutter device based on aforesaid information;wherein,aforesaid exposure control means has a memory means wherein theclassification of subject brightness and timing information for theshutter-closing instruction for each class of subject brightness bothfor prescribed ISO speed are stored as a form of a basic table and saidexposure control means converts aforesaid subject brightness informationcorresponding to the inputted film speed information into theinformation corresponding to aforesaid ISO speed and selects the timinginformation for the shutter-closing instruction from aforesaid basictable based on said converted information, for the exposure; and whereinaforesaid photometry means has a photometry circuit comprising alight-responsive element or a light-responsive element unit that changesthe output in connection with the quantity of light from a subject, aseries system of a capacitor and a comparator that compares the outputof the capacitor with a standard voltage and wherein aforesaid seriessystem of a capacitor is discharged or charged through thelight-responsive element or the light-responsive element unit and thetime period from the start of discharging or charging to the operationof aforesaid comparator is produced as a subject brightness information.2. The camera according to claim 1, wherein aforesaid prescribed ISOspeed is ISO
 100. 3. The camera according to claim 1, wherein aforesaidtiming for the shutter-closing instruction corresponds to the shutteropening operation time.
 4. The camera according to claim 1, whereinaforesaid film speed setting means is provided with a reader that readsthe film speed from the film magazine.
 5. The camera of claim 2 whereinsaid timing for the closing instruction corresponds to the shutter-time.6. A camera comprising:a photometry means that measures the subjectbrightness and produces the measurement results as a subject brightnessinformation; a film speed-setting means that produces the speedinformation of the film to be loaded in the camera; a diaphram-shutterdevice the aperture of which gradually opens from the closed-shuttercondition to the full-open condition and then switches over to theclosing action with a shutter-closing signal; and an exposure controlmeans that receives at least aforesaid subject brightness informationand film speed information and controls the operation of aforesaiddiaphragm-shutter device based on aforesaid information; wherein,aforesaid exposure control means has a memory means wherein a tablecontaining the classification of subject brightness and the timinginformation for the shutter-closing instruction for each class ofsubject brightness both for all the usable film ISO speeds is stored andselects the timing signal for the shutter-closing instructioncorresponding to the subject brightness information from the tablecorresponding to the film speed information inputted, for the exposure;and wherein aforesaid photometry means has a photometry circuitcomprising a light-responsive element or a light-responsive element unitthat changes the output in connection with the quantity of light from asubject, a series system of a capacitor and a comparator that comparesthe output of the capacitor with a standard voltage and whereinaforesaid series system of a capacitor is discharged or charged throughthe light-responsive element or the light-responsive element unit andthe time period from the start of discharging or charging to theoperation of aforesaid comparator is produced as a subject brightnessinformation.
 7. The camera according to claim 6 wherein aforesaid timinginformation for the shutter-closing instruction corresponds to theshutter opening operation time that gives an optimum exposure for theprescribed ISO speed.
 8. A camera comprising:a strobe flash emissiondevice; a judgement means that judges whether the strobe flash emissiondevice is operating or not; a film speed setting means that produces thespeed information of the film loaded in the camera; a photometry meansthat measures the subject brightness and produces the measurementresults as a subject brightness information; a diaphragm-shutter devicethat gradually opens from the closed-shutter condition to the full-opencondition and then switches over to the closing action with ashutter-closing signal; and an exposure control means that receives atleast aforesaid film speed information, aforesaid subject brightnessinformation and the output from aforesaid judgment means and controls,based on aforesaid information, the operation of aforesaiddiaphragm-shutter device and the emission timing of aforesaid strobeflash emission device;wherein, aforesaid exposure control means has amemory means wherein a basic table that contains the classification ofthe subject brightness for the prescribed ISO speed and the timinginformation for the shutter-closing instruction each of whichcorresponds to each of the classification of subject brightness and thatis for the non-use of the strobe flash emission device and another basictable that contains the classification of the subject brightness, thetiming information for the shutter-closing instruction and the timinginformation for the emission of the strobe flash emission device each ofaforesaid timing information corresponds to each of the classificationof the subject brightness and that is for the use of the strobe flashemission device, are stored and said exposure control means converts thesubject brightness information corresponding to the inputted film speedinformation into the information corresponding to aforesaid ISO speedand selects the timing information for the shutter-closing instructioncorresponding to aforesaid converted information in the basic tablecorresponding to the information from aforesaid judgment means and/orthe timing information for the emission of the strobe flash emissiondevice, for the exposure.
 9. The camera according to claim 8, whereinaforesaid prescribed ISO speed is ISO
 100. 10. The camera according toclaim 8, wherein the timing for the shutter-closing instructioncorresponds to the shutter opening operation time.
 11. The cameraaccording to claim 8, wherein aforesaid film speed setting means isprovided with a reader that reads the film speed from a film magazine.12. The camera according to claim 8, wherein aforesaid photometry meanshas a photometry circuit comprising a light-responsive element or alight-responsive element unit that changes relating to the quantity oflight from a subject, a series system of a capacitor and a comparatorthat compares the output of the capacitor with the standard voltage andaforesaid capacitor of series system is discharged or charged throughthe light-responsive element or the light-responsive element unit and atime period from the start of discharging or charging to the operationof aforesaid comparator is produced as a subject brightness information.13. A camera of claim 7 wherein the timing for the closing instructioncorresponds to the shutter-time.
 14. The camera of claim 8 wherein saidemission timing for strobe flash in the case where the strobe flashemission device is used is determined through the smallaperture-priority system.